It's said that 50mm is close to what the human eye sees and is a very versatile focal length in general, especially good for street photography which is what I'm most interested in. That being the case, if I have a cropped sensor (1.6) would I better off with a 35mm prime since it would give me a field of view similar to a 50mm lens (35 X 1.6 = 56) as opposed to a 50mm prime which would give me a field of view similar to an 80mm lens (50 X 1.6 = 80)?
Yes, the nifty fifty for a crop frame would be closer to the 35 prime, but ultimately the order of the day is still choose the lens you need for the shot you want. If you wanted a telephoto shot, then a 50mm wouldn't be the right choice for any sensor size. If you want 50mm effective, then a 35mm prime will give it to you on the crop sensor.
Depending on who you ask, the diagonal field of view (cone of visual attention) of the human eye is somewhere around 54 degrees depending on the person, which is about half-way between those two focal lengths on a full frame sensor. So, in theory, on a crop sensor you should be much wider than 35mm, somewhere around 25mm on a Canon or 28mm on Nikon (or other 1.5 crops) to approximate the FOV of the human eye.
So... If your two choices are 35mm or 50mm, go with the 35mm if you want to be close to this.
The answer totally depends on what you need and what you shoot. If I were you and;
If I'm into street photography, I'd buy 35mm. Also if I were to shoot at narrow places such as indoor parties etc. I'd buy 35mm again.
But if I plan to shoot staged portraits using models/make-up/planning then I'd go for 50mm.
Cropped sensor will give you a view like 1,5x35mm=52,5mm on Nikon and 1.6x35mm and 56mm on Canon that's true. So it's best you go for what you need like I told above. Good luck.